Fluorescent nanosensor based on the synthesis of isoindole and cadmium telluride quantum dots based on Strecker-like method and its application

Abstract

The invention discloses a fluorescent nanosensor based on the Strecker-like method for synthesizing isoindole and combining cadmium telluride quantum dots and its application, which is a composite system composed of 2,3-naphthalene dicarboxaldehyde and potassium sulfite as probe solutions and combined with cadmium telluride quantum dots. Cadmium telluride quantum dots are used as a fluorescence source to emit bright red fluorescence, 2,3-naphthalene dicarboxaldehyde and potassium sulfite are open-type probe solutions, and the addition of carbamate pesticides interacts with 2,3-naphthalene dicarboxaldehyde and potassium sulfite to synthesize an isoindole derivative to emit green fluorescence, thereby realizing the detection of carbamate pesticides based on the ratio fluorescence principle. The nanosensor relies on the fluorescence open-type response detection signal, presenting a significant change from bright red to green fluorescence, having a good visualization effect, and having high sensitivity, good selectivity, strong anti-interference ability, and low detection limit.

Description

Technical Field

[0001] The present invention belongs to the field of pesticide residue detection and food safety, and specifically relates to a fluorescent nanosensor based on a Strecker-like method for synthesizing isoindole and combining cadmium telluride quantum dots, and its application in the detection of carbamate pesticide residues. Background Art

[0002] Carbamate pesticides are the most commonly used pesticides in my country, and some of them are explicitly prohibited from being used on vegetables, fruits, and melons. After entering the body, these pesticides will bind to acetylcholine enzymes, causing acetylcholine in the body's nerve conduction to be unable to be hydrolyzed and over-accumulate, resulting in nerve hyperactivity, followed by symptoms of poisoning, and even death in severe cases. Therefore, how to quickly and quantitatively detect carbamate pesticide residues is of great significance.

[0003] Fluorescence detection is a powerful tool for detecting carbamate pesticide residues due to its fast response, simplicity and high sensitivity. However, most fluorescent sensors currently used for detecting carbamate pesticides are based on enzyme inhibition, which has certain shortcomings in terms of detection conditions, time, cost, etc.; some special actual detection environments interfere with the test results, causing false positives or false negatives. Moreover, most quantitative fluorescence detection methods require professional technicians and expensive, complex and heavy instruments, making it difficult to implement on-site detection. Therefore, there is an urgent need for portable, rapid, on-site, and cost-effective detection technologies. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a fluorescent nanosensor based on the Strecker-like method to synthesize isoindole and combined with cadmium telluride quantum dots and its application in the detection of carbamate pesticide residues. When the fluorescent nanosensor of the present invention is used for quantitative detection of carbamate pesticide residues, it has the advantages of high selectivity, high sensitivity, and visualized quantitative detection.

[0005] The invention discloses a fluorescent nanosensor which synthesizes isoindole based on a Strecker-like method and combines it with cadmium telluride quantum dots. The sensor is a composite system composed of 2,3-naphthalene dicarboxaldehyde and potassium sulfite as probe solutions and combined with cadmium telluride quantum dots.

[0006] In the composite system, the molar concentration ratio of 2,3-naphthalene dicarboxaldehyde, potassium sulfite and cadmium telluride quantum dots is 3750:21875:1.

[0007] The fluorescent nanosensor is prepared by a method comprising the following steps:

[0008] Step 1: Preparation of CdTe quantum dot solution

[0009] 1a. First, tellurium powder (31.9 mg, 0.25 mM) and 0.1 g NaBH 4 (Quickly weigh) Add to a 10 mL two-necked flask, place in an ice bath under a nitrogen atmosphere, and then inject 2 mL of anaerobic water; After stirring for 6 h under a nitrogen atmosphere, the solution color turns light red, forming a NaHTe precursor;

[0010] 1b. CdCl 2 2.5H 2 O (228.4 mg, 1 mmol) was dissolved in 125 mL of ultrapure water and then injected into 210 μL of MPA (2.5 mol), and the pH was adjusted to 9 with 1.0 M NaOH to form a cadmium precursor under stirring and bubbling nitrogen for 30 min to remove dissolved oxygen;

[0011] 1c. Inject 10 mL of dilute sulfuric acid (6.2 M) into the NaHTe precursor solution, and gaseous H 2 Te, gaseous H 2 Te is brought into the cadmium precursor solution, and the solution mixture (final molar ratio: Cd 2+ / Te 2- / MPA=1:0.25:2.5) changed from colorless to light orange, indicating the formation of nuclei of CdTe quantum dots; the mixture was then heated to 400 °C in H 2 The Te gas was completely bubbled and stirred for 15 minutes. The CdTe QDs precursor was refluxed at 100°C for 48 hours to obtain red CdTeQDs crude product. The CdTe QDs crude product solution was purified by ultrafiltration to remove excess thiol precursors, free cadmium ions and by-products, thereby obtaining cadmium telluride quantum dots.

[0012] Step 2: Preparation of ratiometric fluorescent probe solution

[0013] Mix and stir 100 μL of 2,3-naphthalene dicarboxaldehyde solution (0.12 mM) and 100 μL of potassium sulfite solution (0.70 mM, the potassium sulfite aqueous solution should be prepared before use), then add 20 μL of cadmium telluride quantum dot solution (0.16 μM), and then add 2 mL of PBS aqueous solution (pH 9), and use a magnetic stirrer at room temperature for 2 minutes to obtain a fluorescent nanosensor.

[0014] The application of the fluorescent nanosensor of the present invention is to prepare a detection reagent for detecting carbamate pesticide residues.

[0015] The steps include:

[0016] The ratio fluorescence probe solution was taken out and the original bright red fluorescence intensity value (640nm) was recorded. Different concentrations of carbamate pesticide solutions were added to the ratio fluorescence probe system, stirred evenly, and the final concentrations of carbamate pesticides were calculated to be 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 μM (in this system, the molar concentration ratio of 2,3-naphthalenedicarboxylic acid, potassium sulfite, and cadmium telluride quantum dots was 3750:21875:1), reacted at room temperature for 8 minutes, and the fluorescence spectrum of the probe solution in the range of 400-800nm ​​was recorded with 365nm excitation light. By establishing the relationship between the fluorescence intensity and the concentration of carbamate pesticides, the quantitative detection of carbamate pesticides was achieved. At the same time, a series of changes in fluorescence intensity could be presented under ultraviolet light to achieve visual detection.

[0017] The excitation of the sensor fluorescence by the 365 nm excitation light should be the optimal excitation state of the probe solution.

[0018] Furthermore, the ratiometric fluorescent probe of the present invention can be combined with a smart phone to construct a detection platform for the detection of carbamate pesticides, making the detection process more portable and economical.

[0019] The smartphone detection platform includes a multi-well plate, a dark chamber, a 365nm UV lamp, and a smartphone (such as iPhone 13).

[0020] For the operation of the smartphone detection platform, first, the composite fluorescent nanoprobe solution is added to the multi-well plate, and then different concentrations of carbamate pesticide solutions are added. The fluorescent image is obtained by a smartphone in a dark environment and further decomposed into RGB values. Quantitative detection is achieved by installing a color recognition application software (APP).

[0021] The quantitative detection of the smart phone detection platform is obtained by the ratio of the intensity of G and R in the color analysis software.

[0022] The quantitative detection of the smartphone detection platform has three color reading sites, and the reading results are averaged.

[0023] The principle of detecting carbamate pesticides by the ratio fluorescence probe in the present invention is based on the fluorescence opening strategy. Specifically, due to the interaction between 2,3-naphthalene dicarboxaldehyde, potassium sulfite and carbamate, an isoindole derivative is produced. The isoindole derivative has good green fluorescence properties. When used to detect carbamate pesticides, the rapid interaction between 2,3-naphthalene dicarboxaldehyde, potassium sulfite and carbamate causes the green fluorescence to gradually turn on. By establishing the relationship between the fluorescence intensity and the concentration of the carbamate pesticide, the quantitative detection of the carbamate pesticide can be achieved.

[0024] In the present invention, the concentration of carbamate pesticides is continuously increased, and green fluorescence is turned on based on the Strecker-like indole synthesis method, which presents a series of changes in fluorescence intensity under ultraviolet light, thereby realizing visual detection of carbamate pesticides.

[0025] Compared with the existing detection technology, the beneficial effects of the present invention are embodied in:

[0026] 1. The present invention utilizes isoindole substances produced by the Strecker-like indole synthesis method between 2,3-naphthalene dicarboxaldehyde, potassium sulfite and carbamate as fluorescence detection signals for carbamate pesticide residues. Based on the fluorescence opening strategy, it shows obvious changes in fluorescence intensity and realizes visual detection.

[0027] 2. The detection limit of the fluorescent probe solution of the present invention for carbamate pesticide residues on a fluorescence spectrometer is 18.6 nM, which is lower than the permissible limit of carbamate pesticide residues.

[0028] 3. The present invention adopts commercially purchased 2,3-naphthalene dicarboxaldehyde and potassium sulfite, omitting the complicated preparation process.

[0029] 4. By introducing the smartphone detection platform, the use of large instruments can be avoided to a certain extent. Only a portable UV lamp is needed to realize the real-time / on-site visual quantitative detection of carbamate pesticide residues by fluorescent nanosensors, making the detection process portable, fast and low-cost.

[0030] 5. The fluorescent open-type system of 2,3-naphthalenedicarbaldehyde and potassium sulfite prepared by the present invention has good selectivity and sensitivity to carbamate pesticides, can effectively avoid interference from other impurities, and has a fast response. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a transmission electron microscope image of cadmium telluride quantum dots.

[0032] Figure 2 This is a transmission electron micrograph of cadmium telluride quantum dots after adding 2,3-naphthalene dicarboxaldehyde, potassium sulfite and carbamate pesticide residues.

[0033] Figure 3(A) is the fluorescence spectrum and color change diagram of different concentrations of carbamate pesticides on the mixed system of 2,3-naphthalene dicarboxaldehyde, potassium sulfite and cadmium telluride quantum dots. As the concentration of carbamate pesticides increases (from left to right, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 μM), the solution fluorescence gradually changes from bright red to green fluorescence; (B) is the relationship between the fluorescence intensity ratio of the mixed system of 2,3-naphthalene dicarboxaldehyde, potassium sulfite and cadmium telluride quantum dots and the concentration of carbamate pesticides, and the inset is the related chromaticity.

[0034] Figure 4 is a schematic diagram of the operation of the smartphone detection platform (A) and a linear correlation diagram between RGB values ​​and carbamate pesticide concentrations (B).

[0035] Figure 5 Figure 2 shows the selectivity and interference of the fluorescent probe (A) and the corresponding fluorescence color change of the probe solution (B). DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0037] Embodiment 1:

[0038] 1. Preparation of cadmium telluride quantum dot solution

[0039] First, tellurium powder (31.9 mg, 0.25 mM) and 0.1 g NaBH 4 (Quickly weigh) Add to a 10 mL two-necked flask, place in an ice bath under a nitrogen atmosphere, and then inject 2 mL of anaerobic water. After stirring for 6 h under a nitrogen atmosphere, the solution color turns light red, forming a NaHTe precursor;

[0040] In addition, CdCl 2 2.5H 2 O (228.4 mg, 1 mmol) was dissolved in 125 mL of ultrapure water, and then 210 μL MPA (2.5 mol) was injected, and the pH was adjusted to 9 with 1.0 M NaOH. The cadmium precursor was formed under stirring and bubbling nitrogen for 30 min to remove dissolved oxygen;

[0041] When 10 mL of dilute sulfuric acid (6.2 M) was injected into the NaHTe precursor solution, gaseous (H 2 Te), which is brought into the cadmium precursor solution by flowing nitrogen gas, and the solution mixture (final molar ratio: Cd 2+ / Te 2- / MPA=1:0.25:2.5) changed from colorless to light orange, indicating the formation of nuclei of CdTe quantum dots.2 The Te gas was completely bubbled and stirred for 15 minutes. The CdTe QDs precursor was refluxed at 100°C for about 48 hours to obtain crude red CdTeQDs; the crude CdTe QDs solution was purified by ultrafiltration to remove excess thiol precursors, free cadmium ions and by-products, thereby obtaining cadmium telluride quantum dots to be used.

[0042] 2. Preparation of ratiometric fluorescent probe solution

[0043] First, 100 μL of 2,3-naphthalene dicarboxaldehyde solution (0.12 mM) and 100 μL of potassium sulfite solution (0.70 mM) were stirred in a beaker and mixed evenly. Then, 20 μL of the prepared cadmium telluride quantum dots (0.16 μM) were added, and then 2 mL of PBS aqueous solution (pH 9) was added. Then, a magnetic stirrer was used at room temperature for 2 minutes at a constant speed for use.

[0044] 3. Preparation of fluorescent nanosensors

[0045] The ratio probe solution prepared in 2 was taken out, and the original bright red fluorescence intensity value (640nm) was recorded. Then 60μL of carbamate solution of different concentrations was added and the above solution was placed at room temperature for mixing and reacting for 8 minutes before preparation for detection. The fluorescence emission peak at 490nm gradually increased, and the intensity of green fluorescence gradually became stronger, forming a ratio fluorescence sensing system.

[0046] 4. Detection of carbamate pesticides

[0047] Different concentrations of carbamate pesticide solutions are added to the composite fluorescent nanoprobe system, stirred evenly, and the final concentrations of carbamate pesticides are calculated to be 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 μM (in this system, the molar concentration ratio of 2,3-naphthalenedicarboxylic acid, potassium sulfite, and cadmium telluride quantum dots is 3750:21875:1). After 8 minutes of strip reaction at room temperature, the fluorescence spectrum of the probe solution in the range of 400-800 nm is recorded with 365 nm excitation light. By establishing the relationship between the fluorescence intensity and the concentration of the carbamate pesticide, the quantitative detection of the carbamate pesticide is realized. At the same time, a series of changes in fluorescence intensity can be presented under ultraviolet light to realize visual detection.

[0048] 5. Construction of Smartphone Detection Platform

[0049] The smartphone detection platform includes a multi-well plate, a dark chamber, a 365nm UV lamp and a smartphone (iPhone 13).

[0050] For the operation of the smartphone detection platform, first, the composite fluorescent nanoprobe solution is added to the multi-well plate, and then different concentrations of carbamate pesticide solutions are added. The fluorescent image is obtained by a smartphone in a dark environment and further decomposed into RGB values. Quantitative detection is completed by installing a color recognition application (APP).

[0051] Embodiment 2:

[0052] 1. Preparation of cadmium telluride quantum dots

[0053] The preparation process of this step is the same as that of Example 1.

[0054] 2. Preparation of ratiometric fluorescent probe solution

[0055] The preparation process of this step is the same as that of Example 1.

[0056] 3. Preparation of fluorescent nanosensors

[0057] The preparation process of this step is the same as that of Example 1.

[0058] 4. Detection of carbamate pesticides

[0059] The preparation process of this step is the same as that of Example 1.

[0060] 5. Construction of Smartphone Detection Platform

[0061] The preparation process of this step is the same as that of Example 1.

[0062] 6. Drawing of standard curve

[0063] When the excitation light is 365 nm, the fluorescence spectrum of the mixed system in the wavelength range of 400 to 800 nm is recorded, such as Figure 3 As shown in A. Figure 3 B shows the relationship between fluorescence intensity and carbamate pesticide concentration, indicating that when the carbamate pesticide concentration is between 0.1 and 4.5 μM, the fluorescence intensity ratio is linearly related to it, where the horizontal axis is the carbamate pesticide concentration and the vertical axis is I 490 / I 640 The inset is the corresponding chromaticity diagram.

[0064] Embodiment 3:

[0065] 1. Preparation of cadmium telluride quantum dots

[0066] The preparation process of this step is the same as that of Example 1.

[0067] 2. Preparation of ratiometric fluorescent probe solution

[0068] The preparation process of this step is the same as that of Example 1.

[0069] 3. Preparation of fluorescent nanosensors

[0070] The preparation process of this step is the same as that of Example 1.

[0071] 4. Detection of carbamate pesticides

[0072] The preparation process of this step is the same as that of Example 1.

[0073] 5. Construction of Smartphone Detection Platform

[0074] The preparation process of this step is the same as that of Example 1.

[0075] 6. Test of selectivity and interference of composite fluorescent nanoprobe

[0076] Add ions and pesticides (Mg) at a concentration of 10 μM to the composite fluorescent nanoprobe system. 2+ , Ca 2+ 、Zn 2+ , Fe 3+ , cypermethrin, permethrin, malathion, parathion), the results showed that the fluorescence intensity had no obvious change, and then 1 μM of carbamate pesticides was added, and green fluorescence began to appear. The results showed that the system had good selectivity and anti-interference for carbamate pesticides.

Claims

1. A fluorescent nanosensor based on the Strecker-like method for synthesizing isoindole and combining it with cadmium telluride quantum dots, characterized in that: The fluorescent nanosensor is a composite system composed of 2,3-naphthalene dicarboxaldehyde and potassium sulfite as probe solutions and cadmium telluride quantum dots; In the composite system, the molar concentration ratio of 2,3-naphthalene dicarboxaldehyde, potassium sulfite and cadmium telluride quantum dots is 3750:21875:

1.

2. The fluorescent nanosensor according to claim 1, characterized in that The fluorescent nanosensor is prepared by a method comprising the following steps: Step 1: Preparation of CdTe quantum dot solution 1a. First, tellurium powder and NaBH4 were added to a two-necked flask, placed in an ice bath under a nitrogen atmosphere, and then injected with anaerobic water; after stirring for 6 hours under a nitrogen atmosphere, the color of the solution turned light red, forming a NaHTe precursor; 1b, CdCl2·2.5H2O was dissolved in ultrapure water, then injected into MPA, and the pH value was adjusted to 9 with NaOH solution, and a cadmium precursor was formed under stirring and bubbling nitrogen for 30 minutes to remove dissolved oxygen; 1c. A dilute sulfuric acid solution is injected into a NaHTe precursor solution to immediately generate gaseous H2Te, which is then carried into a cadmium precursor solution by flowing nitrogen gas, and the solution mixture changes from colorless to light orange, indicating that nucleation of CdTe quantum dots has been formed; the mixture is then stirred for 15 minutes while the H2Te gas is completely bubbling, and the CdTe QDs precursor is refluxed at 100° C. for 48 hours to obtain a red CdTe QDs crude product; the CdTe QDs crude product solution is purified by ultrafiltration to remove excess thiol precursors, free cadmium ions and by-products, thereby obtaining cadmium telluride quantum dots; Step 2: Preparation of ratiometric fluorescent probe solution The 2,3-naphthalene dicarboxaldehyde solution and the potassium sulfite solution are mixed and stirred evenly, and then the cadmium telluride quantum dot solution is added, and then the PBS aqueous solution is added, and the mixture is mixed evenly to obtain a fluorescent nanosensor.

3. The fluorescent nanosensor according to claim 2, characterized in that: In step 1c, the final molar ratio of the solution mixture is: Cd 2+ / Te 2- / MPA=1:0.25:2.

5.

4. The fluorescent nanosensor according to claim 2, characterized in that: In step 2, 100 μL of 0.12 mM 2,3-naphthalene dicarboxaldehyde solution and 100 μL of 0.70 mM potassium sulfite solution are mixed and stirred evenly, and then 20 μL of 0.16 μM cadmium telluride quantum dot solution is added, and then 2 mL of PBS aqueous solution with a pH of 9 is added, and a magnetic stirrer is used at a uniform speed at room temperature for 2 minutes to obtain a fluorescent nanosensor.

5. The use of the fluorescent nanosensor according to any one of claims 1 to 4, characterized in that: The fluorescent nanosensor is used for preparing a detection reagent for detecting carbamate pesticide residues.

6. The use according to claim 5, characterized in that: The original bright red fluorescence intensity value of the ratio fluorescent probe solution was recorded; then different concentrations of carbamate pesticide solutions were added to the ratio fluorescent probe system, reacted at room temperature for 8 minutes, and the fluorescence spectrum of the probe solution in the range of 400-800nm ​​was recorded with 365nm excitation light. By establishing the relationship between the fluorescence intensity and the concentration of the carbamate pesticide, the quantitative detection of the carbamate pesticide was achieved.

7. The use according to claim 5, characterized in that: The ratio fluorescent probe solution is added to a multi-well plate, and then different concentrations of carbamate pesticide solutions are added. Under ultraviolet light, a series of changes in fluorescence intensity can be presented, achieving visual detection.

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